How to Grant Send on Behalf Permission to Microsoft 365 from On-Premises Shared Mailbox
Question details
Administrators need to grant Send on Behalf permissions from a local, on-premises Exchange shared mailbox to a user mailbox hosted in Microsoft 365.
- Product
- Microsoft Exchange
- Device & OS
- not provided
- Scenario
- Managing cross-premises mailbox delegation in an Exchange Hybrid environment.
- Observed behavior
- Cloud users require the ability to send emails on behalf of an on-premises shared mailbox, which requires specific command-line configurations and directory synchronization.
Ensure that Exchange Hybrid is fully configured between your on-premises organization and Microsoft 365, and that you have administrator access to the on-premises Exchange Management Shell.
Use Exchange Management Shell to Grant Send on Behalf Permissions
Modify the permissions of the on-premises shared mailbox using a PowerShell cmdlet, and then sync the changes to Microsoft 365.
In a hybrid Exchange environment, objects hosted on-premises must be managed from the on-premises Exchange server. You cannot grant this permission directly from the Microsoft 365 admin center.
Log in to your on-premises Exchange server and launch the Exchange Management Shell as an administrator.
Execute the following command, replacing the placeholders with your actual mailbox names: Set-Mailbox "sharedmailboxname" -GrantSendOnBehalfTo @{add='M365 cloud mailbox identity'}
Wait for your scheduled Azure AD Connect directory synchronization to run, or force a manual delta synchronization using PowerShell on your Azure AD Connect server.
Allow sufficient time for the updated attributes to process in Exchange Online, then verify that the cloud user can successfully send emails on behalf of the shared mailbox.
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Frequently Asked Questions
Can I grant Send on Behalf permissions using the Microsoft 365 Admin Center?
No. If the shared mailbox is hosted on-premises, its attributes are mastered locally. You must make the changes in your on-premises Exchange environment and sync them to Microsoft 365.
Why is the cloud user receiving a bounce-back error when trying to send on behalf?
This usually happens if directory synchronization has not yet completed, or if the Global Address List (GAL) hasn't updated in the user's Outlook client. Wait for synchronization and have the user download the latest Offline Address Book (OAB).
What is the difference between 'Send As' and 'Send on Behalf'?
'Send As' allows a user to send an email that appears exactly as if it came from the shared mailbox. 'Send on Behalf' clearly indicates to the recipient that the email was sent by a specific user on behalf of the shared mailbox.
